The present invention relates to a bridge-less step-up switching power supply devices capable of reducing a switching loss of a switching element.
There is known a bridge-less step-up switching power supply device for improving a power factor without rectifying an AC voltage of an AC power supply. FIG. 1 shows an example of a related-art bridge-less step-up switching power supply device. In FIG. 1, a series circuit of a reactor L11 and a switch Q1 including a MOSFET is connected between one end of an AC power supply Vin and an output voltage (−Vo). A series circuit of a reactor L12 and a switch Q2 including a MOSFET is connected between the other end of the AC power supply Vin and the output voltage (−Vo).
An anode of a diode D1 is connected to a connection point of the reactor L11 and a drain of the switch Q1, and a cathode of the diode D1 is connected to an output voltage (+Vo) and one end of a capacitor C1. An anode of a diode D2 is connected to a connection point of the reactor L12 and a drain of the switch Q2, and a cathode of the diode D2 is connected to the output voltage (+Vo) and one end of the capacitor C1. The other end of the capacitor C1 is connected to the output voltage (−Vo). A load (not-illustrated) is connected between the output voltage (+Vo) and the output voltage (−Vo).
A controller 100 controls the output voltage Vo so as to be a predetermined voltage by simultaneously turning on/off the switch Q1 and the switch Q2 based on a voltage of the capacitor C1.
Such a related-art bridge-less step-up switching power supply device combines rectification and step-up operations of an AC voltage, and can significantly reduce a conduction loss due to a diode bridge in a related-art power supply circuit, and therefore is used as a high-efficient power supply device.
As such a related art, a power supply device described in Japanese Patent Application Laid-Open Publication No. 07-115774 (Patent Literature 1) is known. In this power supply device, two rectification elements, through which a feedback current passes, of a bridge-type full-wave rectifying circuit are replaced with a high speed switch element, respectively, and the high speed switch elements are properly controlled, thereby improving a power factor, reducing the number of components, and improving the conversion efficiency/reliability.